Study On Photographic Properties Of Photothermographic Materials Based On Silver Tolyltriazole

In recent years, significant advances have been made in the technology of Photothermographic (PTG) imaging materials and medical films fields. However, its sensitivity is still too low to meet the application in high sensitivity fields. To solve this problem, some new methods to improve sensitivity based on hydrophilic PTG materials were applied and mechanisms of some influences on photographic properties were also preliminarily discussed in this dissertation. The main results were summarized as follows:1. Preparation of PTG materials. This new PTG system composed of hydrophilic polyvinyl alcohol (PVA) as binder, in-situ or ex-situ formed AgBr as photo-sensitive element, silver tolyltriazole (AgTTA) as silver source, pyrogallic acid as developer, as well as other functional components. The results showed that the image density was moderate and fog density kept low, so the PTG materials were fit for further study to improve sensitivity.2.Study on the Thermochromism of Nickel Stearate and Pyrogallic Acid The variation of the optical density of polyvinyl alcohol coating of NiSt2 and PGA with temperature raising and time prolonging was studied. The results showed that the density increased linearly with temperature raising and time prolonging, and the mixture were stable in low temperature and achieved thermochromism in high temperature. A new and practical thermographic material will be provided if the speed of development is further improved. According to UV-Vis absorption spectrum, we deduced that a molecular compound may have been formed by NiSt2 and PGA during the heating process, and this molecular compound may form one or more kinds of molecular congeries in solvent with increasing its concentration.3.The influence of metallic stearates on the photographic properties of PTG materials based on in-site formed AgBr as photo-sensitive element The effect of stearates'amount on the photographic properties of PTG materials was studied. The results showed that the stearates could improve the sensitivity of PTG materials. The addition of NiSt2 greatly increased the maximum density and the sensitivity together with a slight fog increase. However the addition of BaSt2 and CaSt2 did not make such great increase in the maximum density and the sensitivity, together with a slight fog decrease. The study of the influence of system on pH, [Ag+] and cation showed that NiSt2 could be as an accelerator because melting point of NiSt2 is low. In development process, Ni2+ from NiSt2 replaced more Ag+ of AgTTA and accelerated the forming of AgSt, so NiSt2 accelerated development more obviously. It may be the direct reason that nickel stearate acts as a more effective accelerator than barium stearate and calcium stearate.4. The influence of metallic stearates on the photographic properties of PTG materials based on ex-site formed AgBr as photo-sensitive element The effects of amount of AgBr and stearates on the photographic properties of PTG materials were studied, and we analyzed different influences between nickel stearate and barium stearate during the process of latent imaging formation and development. The results showed that the maximal sensitivity of PTG materials could be obtained when the ratio of AgBr to AgTTA was 0.25, and the sensitivity of PTG materials with nickel stearate was 1.1 times higher and with barium stearate was 4 times higher than the primitive one. In the process of latent imaging formation, nickel stearate may result in latent image dispersing, which is not benefit to improve the sensitivity, but silver stearate formed by barium stearate and AgTTA may accelerate the development. On the other hand, barium stearate can control the fog, so the sensitivity increases fast but the fog increases slowly.5.The influence of traditional chemical sensitization on the photographic properties of PTG materials The influence of photographic properties on AgBr that sensitized by sulfur, gold, sulfur plus gold and dimethylamine borane (DMAB) and tetramethylthioharnstoff (TMT) in different mode were studied. The result showed that traditional chemical sensitivity that used in PTG system was an effective method to improve the sensitivity. Fog was not increased while sensitivity was improved, and the effects of sulfur plus gold and DMAB were the best. The effect of TMT as a traditional sulfur sensitizer was more effective in PTG materials. IR absorption spectrum and pAg showed that TMT and AgTTA may form a more difficult dissolvable silver salt complex that reduced the concentration of interstitial silver ion, which increase the efficiency of latent image formation, so the sensitivity was improved.